全文获取类型
收费全文 | 3456篇 |
免费 | 568篇 |
国内免费 | 441篇 |
专业分类
测绘学 | 1365篇 |
大气科学 | 320篇 |
地球物理 | 930篇 |
地质学 | 815篇 |
海洋学 | 342篇 |
天文学 | 51篇 |
综合类 | 427篇 |
自然地理 | 215篇 |
出版年
2024年 | 9篇 |
2023年 | 35篇 |
2022年 | 117篇 |
2021年 | 136篇 |
2020年 | 135篇 |
2019年 | 230篇 |
2018年 | 129篇 |
2017年 | 216篇 |
2016年 | 192篇 |
2015年 | 199篇 |
2014年 | 190篇 |
2013年 | 233篇 |
2012年 | 253篇 |
2011年 | 252篇 |
2010年 | 171篇 |
2009年 | 230篇 |
2008年 | 221篇 |
2007年 | 239篇 |
2006年 | 226篇 |
2005年 | 174篇 |
2004年 | 162篇 |
2003年 | 130篇 |
2002年 | 106篇 |
2001年 | 80篇 |
2000年 | 74篇 |
1999年 | 66篇 |
1998年 | 62篇 |
1997年 | 40篇 |
1996年 | 33篇 |
1995年 | 29篇 |
1994年 | 24篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有4465条查询结果,搜索用时 46 毫秒
991.
Collocation-PECE�㷨�ڵ����Ǿ��ܶ����е�Ӧ�� 总被引:1,自引:1,他引:0
???????????У?PECE????????????????????????????Collocation????????????????幫??????????μ?PECE???????????????????ж??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????Adams-PECE????????PECE?????????????????????????????,???????????Collocation-PECE??????????????н???????????????Ч?? 相似文献
992.
993.
波阻抗遗传算法反演方法的研究及应用 总被引:3,自引:3,他引:3
作者介绍的遗传算法是在自然界生物遗传过程优选和进化原理的基础上,针对波阻抗反演的实际问题,对标准的遗传算法进行了改进,引入了模拟退火算法中的热槽法控制初始群体的产生,用逐位迭代的交换方式代替传统的杂交方式即随机选择杂交点进行交换。使用改进的遗传算法对地震波阻抗进行反演,可很好地提高反演的精度。在文中最后,作者通过理论模型和实例验证了上述的思想。 相似文献
994.
Using geographic information system to study flooded area and damage evaluation has been a hotspot in environmental disaster research for years. In this paper, a model for flooded area calculation and damage evaluation is presented. Flooding is divided into two types: ‘source flood’ and ‘non-source flood’. The source-flood area calculation is based on seed spread algorithm. The flood damage evaluation is calculated by overlaying the flooded area range with thematic maps and relating the result to other social and economic data. To raise the operational efficiency of the model, a skipping approach is used to speed seed spread algorithm and all thematic maps are converted to raster format before overlay analysis. The accuracy of flooded area calculation and damage evaluation is mainly dependent upon the resolution and precision of the digital elevation model (DEM) data, upon the accuracy of registering all raster layers, and upon the quality of economic information. This model has been successfully used in the Zhejiang Province Comprehensive Water Management Information System developed by the authors. The applications show that this model is especially useful for most counties of China and other developing countries. 相似文献
995.
Electrokinetic phenomena associated with a water injection experiment at the Nojima fault on Awaji Island, Japan 总被引:2,自引:0,他引:2
Hideki Murakami Takeshi Hashimoto Naoto Oshiman Satoru Yamaguchi Yoshimori Honkura Norihiko Sumitomo 《Island Arc》2001,10(3-4):244-251
Abstract Self-potential variations were measured to estimate the magnitude of electrokinetic and hydrological parameters (zeta potential and permeability) of the Nojima Fault zone in Awaji, Japan. The study observed self-potential variations that seemed to be associated with water flow from the injection well to the fracture zone, which were induced by turning the injection on and off. Amplitudes of the variations were a few to 0.03 V across 320–450 m dipoles. These variations can be explained well with an electrokinetic model. The quantity k/ζ (permeability/zeta potential) is in the range 1.6 × 10−13 − 5.4 × 10−13 m2 /V. Permeability of the Nojima fault zone can be estimated as approximately 10−16 –10−15 m2 on the assumption that the zeta potential is in the range –0.01 to –0.001 V. 相似文献
996.
The restriction of the Babuska–Brezzi stability criteria for the mixed formulation requires non-uniform interpolation of displacement and pore-pressure variables, which complicates the coding in the finite element analysis. This will certainly preclude the use of many otherwise useful elements. A possible solution to overcome this problem introduced earlier by the authors requires a semi-explicit form. However, the effectiveness of the semi-explicit procedure is dependent on the time step length used, which presents difficulties for transient analysis. In this paper, an unconditionally stable staggered implicit-implicit algorithm is developed, which is generalised from the semi-explicit form. For non-uniform mesh configurations, the results indicate a significant improvement compared with those obtained by using the semi-explicit procedure. 相似文献
997.
IntroductionAfter scientists at home and abroad have studied for many years, most of them take streaming potential (SP) as the most possible mechanism for the generation of self-potential anomaly during earthquake preparation. SP refers to electric signal, which generates local or regional electric field, produced when a fluid flows in a porous medium, as a sequence of the change of crustal stress or strain. Many facts suggest that SP is the most possible mechanism of generating self-potenti… 相似文献
998.
强震前中期地震活动的变化及TIP预测研究 总被引:2,自引:0,他引:2
用改进的M8算法研究了1979年以来我国华北西南及邻近地区共16次强震前的TIP,即震发生概率增长时间。结果表明,14次强震发生在补判定为概率增长时间的TIP内。TIP警戒约占研究部时空域的37%,获得了较好的强震中期预测内符效果。表明该方法可作为强震中期预测的手段之一。 相似文献
999.
In this paper, equations of atmospheric and oceanic dynamics are reduced to a kind of evolutionary equation in operator form, based on which a conclusion that the separability of motion stages is relative is made and an issue that the tractional splitting methods established on the physical separability of the fast stage and the slow stage neglect the interaction between the two stages to some extent is shown. Also, three splitting patterns are summed up from the splitting methods in common use so that a comparison between them is carried out. The comparison shows that only the improved splitting pattern (ISP) can be in second order and keep the interaction well. Finally, the applications of some splitting methods on numerical simulations of typhoon tracks made clear that ISP owns the best effect and can save more than 80% CPU time. 相似文献
1000.
Li Wang 《Mathematical Geology》1995,27(7):847-865
This paper presents a test of the automatic identification of photomicrographs of rocks in thin sections using digital image processing and texture analysis. Three sets of textural measures derived respectively from the cooccurrence matrix, texture space, and texture spectrum have been used to identify six rock types (mylonite, diorite porphyry, diorite. gabbro, granite, and peridotite). Exploring only the texture characteristics of images, the average correct recognition rate reaches 89% for 58 photographs belonging to the six types. The results also show the importance of using those more discriminating texture features in the classification algorithm. For the present study, the average rate of correct classification ranges from 46% to 89% depending on the set of texture measures used. The features extracted from the texture spectrum have more discriminating performance than the conventionally used Haralick measures derived from the cooccurrence matrix. 相似文献